Field of the Invention
The present invention relates generally to an electromechanical drive system for a medication infusion system, and more particularly to a medication infusion system having a disposable cassette containing a fluid pump and active valves which cassette is mounted on and driven by a main pump unit which includes a prime mover and a drive mechanism, the drive mechanism using a single power module cam to drive both the pump and the valves.
In the past there have been two primary techniques which have been used to deliver drugs which may not be orally ingested to a patient. The first such technique is through an injection, or shot, using a syringe and needle which delivers a large dosage at relatively infrequent intervals to the patient. This technique is not always satisfactory, particularly when the drug being administered is potentially lethal, has negative side effects when delivered in a large dosage, or must be delivered more or less continuously to achieve the desired therapeutic effect. This problem results in small injections being given at more frequent intervals, a compromise approach not yielding satisfactory results.
Alternatively, the second technique involves administering a continuous flow of medication to the patient, typically through an IV bottle. Medication may also be delivered through an IV system with an injection being made into a complex maze of IV tubes, hoses, and other paraphernalia. With drop counters being used to meter the amount of bulk fluid delivered, many medications still end up being administered in a large dosage through an injection into the IV lines, although the medications may be diluted somewhat by the bulk fluid.
As an alternative to these two techniques of administering medication to a patient, the relatively recent addition of medication infusion pumps has come as a welcome improvement. Medication infusion pums are utilized to administer drugs to a patient in small, metered doses at frequent intervals or, alternatively, in the case of some devices, at a low but essentially continuous rate. Infusion pump therapy may be electronically controlled to deliver precise, metered doses at exactly determined intervals, thereby providing a beneficial gradual infusion of medication to the patient. In this manner, the infusion pump is able to mimic the natural process whereby chemical balances are maintained more precisely by operating on a continuous time basis.
One of the requirements of a medication infusion system is dictated by the important design consideration of disposability. Since the portion of the device through which medication is pumped must be sterile, in most applications of modern medication infusion equipment some portions of the equipment are used only once and then disposed of, typically at regular intervals such as once daily. It is therefore desirable that the fluid pump portion of the infusion pump device be disposable, with the fluid pump being designed as an attachable cassette which is of inexpensive design, and which is easily installable onto the main pump unit.
It will be perceived that it is desirable to have a simple disposable cassette design to minimize the cost of construction of the cassette, using the minimum number of parts necessary in the design of the cassette. The design of the cassette must be mass producible, and yet result in a uniform cassette which is capable of delivering liquid medication or other therapeutic fluids with a high degree of accuracy. The cassette should include therein more than just a fluid pump; other features which has formerly been included in peripheral devices may be included in the cassette.
It is therefore the primary objective of the present invention to provide a drive system in a main pump unit for driving a reciprocating fluid pump having active inlet and outlet valves, the pump and valves being contained in the disposable cassette. The system must be highly sophisticated while mechanically uncomplex and inherently reliable. Specifically, the drive system of the present invention shall be capable of driving a pump with a high degree of precision and accuracy, with the degree of precision remaining constant throughout the extended operating life of the main pump unit.
Several other additional features are desirable in the design of a cassette and a main pump unit making up an infusion system. Such features include a simple and uncomplicated installation of the cassette onto the main pump unit, and a wide range in the volume which may be pumped by the system over a particular period of time. It is an objective of the present invention that the valves and the pump be incapable of being operated out of synchrony, and it that they always be properly synchronized. Another objective of the present invention is to prevent free flow of fluid through an installed cassette. Still another objective of the present invention is that the valves in the cassette be placed in position to be driven by the drive system by merely installing the cassette with the valves in proximity to the drive mechanism. In addition, the drive system must be capable of varying output over a broad range while retaining a high degree of accuracy across the complete range of delivery rates. No system currently known in the art has satisfactorily accomplished all of these objectives.
Despite the inclusion of more features than contained in any competing design, both the main pump unit and the cassette of the present invention shall utilize a minimum number of parts, all of the parts are of inexpensive construction yet which afford the assembled cassette the high degree of accuracy which must be retained. The system of the present invention must have other advantages necessary to compete effectively against known competing designs. The system must provide an ease of use rivaling the best of such competing systems. It must accomplish all these objects in a manner which will retain all of the advantages of reliability, durability, and safety of operation. The drive system of the present invention must provide all of these advantages and overcome the limitations of the background art without incurring any relative disadvantage. All the advantages of the present invention will result in a superior medication infusion system having a number of advantages making the system a highly desirable alternative to systems presently available.